The null hypothesis for this study is that there is no difference in outcome comparing pregnancies with sonographically documented uterine synechiae to those without synechiae. A retrospective case-control study was performed to test this hypothesis. The cases and controls were part of a population of 29,543 patients who underwent ultrasonographic examination at our institution between March 1988 and March 1995. The cases of synechiae were determined by the sonographic finding of a shelflike protrusion into the amniotic cavity. Each case was matched to controls. Matching criteria were maternal age, gestational age at scan, and type of invasive procedure if applicable. Outcome data were obtained by review of medical records and patient and physician interviews. Statistical analysis was performed using the chi-square analysis with Yates correction. Odds ratios were calculated. The overall prevalence of uterine synechiae was 0.47% (140 of 29,543) in the scanned population. No significant difference was found between cases and controls with respect to maternal age, reproductive losses, and medical problems. The mean gestational age at time of diagnosis was 18.3 +/- 4.2 weeks. No difference in outcome existed between cases and controls except for mean birth weight. We conclude that the presence of uterine synechiae does not appear to confer an increased risk for poor pregnancy outcome or for malpresentation.